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Streams, Structures, Spaces, Scenarios, Societies (5S): A Formal Model for Digital Libraries
No full textDigital libraries (DLs) are complex information systems and therefore demand formal foundations lest development efforts diverge and interoperability suffers. In this paper, we propose the fundamental abstractions of Streams, Structures, Spaces, Scenarios, and Societies (5S), which contribute to define digital libraries rigorously and usefully. Streams are sequences of abstract items used to describe static and dynamic content. Structures can be defined as labeled directed graphs, which impose organization. Spaces are sets of abstract items and operations on those sets that obey certain rules. Scenarios consist of sequences of events or actions that modify states of a computation in order to accomplish a functional requirement. Societies comprehend entities and the relationships between and among them. Together these abstractions relate and unify concepts, among others, of digital objects, metadata, collections, and services required to formalize and elucidate “digital librariesâ€. The applicability, versatility and unifying power of the theory is demonstrated through its use in three distinct applications: building and interpretation of a DL taxonomy, analysis of case studies of digital libraries, and utilization as a formal basis for a DL description language
Using Interactive Maps in Community Applications
Get PDFInteractive maps provide unique ways to support community applications. In particular, they enable new collaborative activities. Map-based navigation supports a community environment as well as virtual tours. Interactive maps can also function as a tool in collecting historical information and discussing new spatial layouts. These examples indicate the numerous opportunities for interactive maps to support collaboration
Empirical Comparisons of Virtual Environment Displays
Get PDFThere are many different visual display devices used in virtual environment (VE) systems. These displays vary along many dimensions, such as resolution, field of view, level of immersion, quality of stereo, and so on. In general, no guidelines exist to choose an appropriate display for a particular VE application. Our goal in this work is to develop such guidelines on the basis of empirical results. We present two initial experiments comparing head-mounted displays with a workbench display and a foursided spatially immersive display. The results indicate that the physical characteristics of the displays, users' prior experiences, and even the order in which the displays are presented can have significant effects on performance
Testbed Evaluation of Virtual Environment Interaction Techniques
No full textTestbed Evaluation of Virtual Environment Interaction Technique
Probability-one Homotopies in Computational Science
Get PDFProbability-one homotopy algorithms are a class of methods for solving nonlinear systems of equations that,under mild assumptions,are globally convergent for a wide range of problems in science and engineering.Convergence theory, robust numerical algorithms,and production quality mathematical software exist for general nonlinear systems of equations, and special cases suc as Brouwer fixed point problems,polynomial systems,and nonlinear constrained optimization.Using a sample of challenging scientific problems as motivation,some pertinent homotopy theory and algorithms are presented. The problems considered are analog circuit simulation (for nonlinear systems),reconfigurable space trusses (for polynomial systems),and fuel-optimal orbital rendezvous (for nonlinear constrained optimization).The mathematical software packages HOMPACK90 and POLSYS_PLP are also briefly described
A Probability-one Homotopy Algoithm for Non-Smooth Equations and Mixed Complementarity Problems
Get PDFA probability-one homotopy algorithm for solving nonsmooth equations is described. This algorithm is able to solve problems involving highly nonlinear equations,where the norm of the residual has non-global local minima.The algorithm is based on constructing homotopy mappings that are smooth in the interior of their domains.The algorithm is specialized to solve mixed complementarity problems through the use of MCP functions and associated smoothers.This specialized algorithm includes an option to ensure that all iterates remain feasible.Easily satisfiable sufficient conditions are given to ensure that the homotopy zero curve remains feasible,and global convergence properties for the MCP algorithm are developed.Computational results on the MCPLIB test library demonstrate the effectiveness of the algorithm
From Landscapes to Waterscapes: A PSE for Landuse Change Analysis
Get PDFWe describe the design and implementation of L2W — a problem solving environment (PSE) for landuse change analysis. L2W organizes and unifies the diverse collection of software typically associated with ecosystem models (hydrological, economic, and biological). It provides a web-based interface for potential watershed managers and other users to explore meaningful alternative land development and management scenarios and view their hydrological, ecological, and economic impacts. A prototype implementation for the Upper Roanoke River Watershed in Southwest Virginia, USA is described
A fully Distributed Parallel Global Search Algorithm
Get PDFThe n-dimensional direct search algorithm DIRECT of Jones,Perttunen, and Stuckman has attracted recent attention from the multidisciplinary design optimization community. Since DIRECT only requires function values (or ranking)and balances global exploration with local refinement better than n-dimensional bisection, it is well suited to the noisy function values typical of realistic simulations. While not efficient for high accuracy optimization, DIRECT is appropriate for the sort of global design space exploration done in large scale engineering design. Direct and pattern search schemes have the potential to exploit massive parallelism, but efficient use of massively parallel machines is nontrivial to achieve. This paper presents a fully distribute control version of DIRECT that is designed for massively parallel (distribute memory architectures. Parallel results are presented for a multidisciplinary design optimization problem — configuration design of a high speed civil transport
Theory of Globally Convergent Probability-one Homotopies for Non-linear Programming
Get PDFFor many years globally convergent probability-one homotopy methods have been remarkably successful on difficult realistic engineering optimization problems,most of which were attacked by homotopy methods because other optimization algorithms failed or were ineffective. Convergence theory has been derived for a few particular problems,and considerable fixed point theory exists,but generally convergence theory for the homotopy maps used in practice for nonlinear constrained optimization has been lacking.This paper derives some probability-one homotopy convergence theorems for unconstrained and inequality constrained optimization,for linear and nonlinear inequality constraints,and with and without convexity.Some insight is provided into why the homotopies used in engineering practice are so successful,and why this success is more than dumb luck.By presenting the theory as variations on a prototype probability-one homotopy convergence theorem,the essence of such convergence theory is elucidated
Probability-one Homotopy Algorithms for Solving the Coupled Lyapunov Equations Arising in Reduced-Order H^2/H^(infinity) Modeling, Estimation, and Control
No full textoai:vtcstechreports.OAI2:1Optimal reduced order modeling, estimation, and control with respect to combined H^2/H^(infinity) criteria give rise to coupled Lyapunov and Riccati equations. To develop reliable numerical algorithms for these problems this paper focuses on the coupled Lyapunov equations which appear as a subset of the synthesis equations. In particular, this paper systematically examines the requirements of probability-one homotopy algorithms to guarantee global convergence. Homotopy algorithms for nonlinear systems of equations construct a continuous family of systems and solve the given system by tracking the continuous curve of solutions to the family. The main emphasis is on guaranteeing transversality for several homotopy maps based upon the pseudogramian formulation of the coupled Lyapunov equations and variations based upon canonical forms. These results are essential to the probability-one homotopy approach by guaranteeing good numerical properties in the computational implementation of the homotopy algorithms